1. Field of the Invention
The invention relates to a sound receiving process and to a sound receiving arrangement.
2. Description of Related Art
Efforts made so far to design a xe2x80x9ctruexe2x80x9d digital microphone without analog intermediate step have not proceeded past theoretical ideas. On the basis of these ideas, the position or movement of a sound receptor (e.g. a diaphragm) for an electroacoustic sound source is measured, either optically or by means of ultrasound, e.g. by evaluating interference patterns or transit time effects, wherein a counting operation is used, among other things, to digitize the measured information. Such a process if disclosed, for example, in the GB-A-1 077 074. The sound is picked up via two sound receptors, which are connected in series acoustically in the direction of the incoming sound. The signal voltages given off both sound receptors are displaced by an amount that follows from the sound transit time between the two sound receptors, which are arranged at a specified distance. By comparing and digitizing these two signals, a 1-bit DPCM signal is generated, which is then transmitted to an up/down counter for conversion to a bit-parallel digital signal.
Converters have in the meantime become available for the purely electrical conversion from analog audio signals to a corresponding digital signal, which for the most part meet the special requirements for converting audio signals. Above all, this refers to a high resolution, linearity and low inherent noise. In particular, Sigma-Delta converters achieve these characteristics, as is disclosed, for example, in the references U.S. Pat. No. 5,181,032 and U.S. Pat. No. 5,191,332. With the known Sigma-Delta converters, the audio signal is fed into a control circuit, wherein the feedback counter-coupling signal is conducted via a 1-bit or a traditional multi-bit AD converter and a corresponding inverse converter. In the generated digital 1-bit or multi-bit data current, the analog audio signal information is represented by the time ratio of the digital 0/1 states. The desired digital output signal is obtained by means of digital filtering and reformatting. Such a control circuit system represents a modulator that is synchronized with a supplied clock pulse, wherein favorable noise and resolution qualities are achieved by splitting the information in the modulator into several signal paths and a varied signal treatment.
However, all known converters for generating a digital signal from an acoustic signal are unsuitable for studio microphones because they cannot compete with analog studio microphones with respect to dynamic range, noise level and sufficient quantization.
In contrast, it is the object of the invention to specify a process and a sound receiving arrangement, which makes it possible to directly convert an acoustic signal, acting upon the sound receptor of a sound receiver, to a digital information, thereby meeting the requirements with respect to dynamic range, noise and sufficient quantization.
This object and other objects are addressed by the inventive process and apparatus.
In a first embodiment, the invention comprises a process for converting an acoustic signal, acting upon the sound receptor of a sound receiver, to an electrical signal. In the inventive method, if the acoustic signal acts upon the sound receptor, the sound receptor is also acted upon by a counter-signal, such that the sound receptor remains mostly in its resting state. The counter-signal is derived from a control variable of a control circuit of which the sound receiver is a component. The control variable contains information on the acoustic signal, and each deviation of the receptor from its resting state generates digital information (xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d).
In a further embodiment, the invention comprises a sound receiving arrangement. The sound receiving arrangement comprises a sound receiver including a sound receptor. In the inventive sound receiving arrangement, if the acoustic signal acts upon the sound receptor, the sound receptor is also acted upon by a counter-signal, such that the sound receptor remains mostly in its resting state. The counter-signal is derived from a control variable of a control circuit of which the sound receiver is a component. The control variable contains information on the acoustic signal, and each deviation of the receptor from its resting state generates digital information (xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d).
The invention is based on the idea of retaining the capacitive converter principle, unsurpassed so far with respect to dynamic scope and noise behavior, of a xe2x80x9ctruexe2x80x9d digital microphone. The known and mature technology of the capacitive converter can be fully incorporated with this. The capacitive converter is incorporated into a digitizing conversion process, in such a way that the receptor (e.g. a capacitor diaphragm), upon which the acoustic signal acts as sound pressure, is not deflected proportional to the signal strength, but according to the invention is kept almost in the rest state through a counter-acting sound signal or a counter force. The counter-signal is derived from the control variable of a control circuit, of which the sound receiver is a component, wherein the control variable contains the information on the acoustic signal. As compared to the known capacitor microphones and owing to the fact that the receptor for the most part remains in its reverberative rest state, characteristic errors that depend on the receptor position and lead to signal distortions, as well as mechanical self-resonances of the receptor that influence the frequency course and the impulse behavior of the electrical output signal for all practical purposes are no longer effective. Also, the invention practically no longer requires measures for a passive damping of the receptor, such as are required for linearizing known capacitor microphones by taking into account a reduction in the sensitivity, so that the sensitivity of a converter designed according to the invention is clearly improved. It is essential that the remaining slight deflections of the receptor are evaluated so as to provide only information on the direction of the deviation from the rest state and that this information is displayed as xe2x80x9czeroxe2x80x9d or xe2x80x9cone.xe2x80x9d It means that the comparator function as elementary function of each analog/digital conversion process is carried out directly at the sound receptor, without requiring an analog intermediate signal obtained from the sound receiver.